Sadly no support for Parallels.
The docker team completely ignored the great work the parallels team put into creating a parallels driver instead telling them to wait for the plugin architecture to be finished. Reference: https://github.com/docker/machine/pull/939
The Machine maintainers are overwhelmed by pull requests adding new drivers. They are worried about maintenance load, and its impact on the quality of drivers over time. So instead of making promises they can't deliver on, they're investing the time on a plugin architecture, so that everyone can create and add their own drivers without depending on the bottleneck that is the core maintainers.